Removing solvents from raffinates



N v- 1941- J. L. FWKUN, JR 2,261,799

REMOVING SOLVENTS FROM RAFFINATES Filed Nov. 30, 1939 Patented Nov. 4,1941 REMOVING SOLVENTS FROM RAFFINATES Joe L. Franklin, Jr., GooseCreek, Tex.,'assignor to Standard Oil Development Company, a.corporation of Delaware Application November 30, 1939, Serial No.306,829

4 Claims.

The present invention relates to the solvent treatment of mineral oils.The invention is particularly directed to the recovery of the primaryselective solvent from the oil without the necessity of distillation. Inaccordance with the present invention the extracted oil is re-extractedwith a secondary solvent which has a preferential selectivity for theprimary solvent as compared, to the mineral oil and which is furthercharacterized by having a boiling point above the boiling point of theprimary solvent.

It is well known in the art to treat petroleum oils with variousselective solvents or solvent mixtures which have the ability tosegregate the relatively more parafiinic constituent from the relativelymore aromatic constituents. In these processes solvents of the class ofsolvents which have a preferential selectivity for the more aromatictype compounds are usually employed. Solvents of this class are, forexample, phenol, furfural, nitro benzene, sulfur dioxide, cresol,aniline, beta beta dichlor diethyl ether, and the like. It is also knownto employ other substances as, for example, substances of the class ofliquefled normally gaseous hydrocarbons, in combination with the abovedescribed class of solvents. In these solvent treating processes the oiland the solvent are contacted by various means, as for example, by batchor by semi-batch operations. However, the usual method of treating theoil with the solvent is to contact the oil and solvent in acountercurrent treating tower process in which the heavier phase,usually the solvent, is introduced at the top of a countercurrenttreating tower, while the lighter phase, usually the oil, is introducedat the center or at the bottom section of the tower. Efiicient contactbetween the countercurrently flowing phases is secured by suitabledistributing and contacting means such as contact masses, distributingplates, pierced plates and the like. Temperature and pressure conditionsare maintained in the tower to secure the formation of a relativelysolvent .poor or raflinate phase highly paraffinic in nature and asolvent-rich or solvent extract phase highly aromatic in nature. Therespective phases are segregated and removed from the tower. The solventis then separated from the extract and rafiinate by anysuitable means,usually by distillation.

In these processes a large part of the costs of the operations is in therecovery of the selective solvents. As a result, many procedures havebeen suggested for recovering the selective solvent from the treated oilwithout the necessity of distillation. For instance, it has beensuggested that the solvent extract phase be re-extracted with asecondary solvent which has a preferential selectivity for the oil ascompared to the primary selective solvent. A process of this characteris to treat petroleum oils with a phenolic type solvent and then tore-extract the resulting solvent extract phase with a narrow cut naphthasolvent boiling in the range from 300. F. to 500 F., and having apreferential selectivity for the extract oilas compared to the primaryphenolic solvent. The secondary solvent is then usually removed from theextract by distillation. This type of operation possesses advantagesover prior processes, since the latent heat of vaporization of thesecondary solvent is less than the latent heat of vaporization of theprimarysolvent, as for example, phenol. Processes of this character,however, have notbeen entirely successful due to the fact that the veryhighly aromatic oil constituents are more soluble in the primary solventthan they are in the secondary solvent and are therefore not readilyremoved from the primary solvent. The result is that the highly aromaticoil constituents continually build up in the primary solventnecessitating frequent purification of the same. Furthermore theseprocesses directed to the removal of the primary selective solvent fromthe solvent extract phase by means of a secondary solvent are notsuitable for separating raflinate oil from the primary solvent in theprimary ramnate phase.

I have now discovered a process by whichv it is possible to treatmineral oils with solvents ofthe class which have a preferentialselectivity for the more aromatic type constituents as compared to themore parafiinic type constituents and to separate these solventsfrom'the raflinate oil without having to distill the same. In accordancewith my invention the valuable raflinate oilis recovered withoutdistillation thus ensuring substantially no decomposition of the same byre-extracting the rafilnate phase with a secondary solvent selectedfrom'a particular classof sub stances. My process utilizes a secondarysolvent selected from the class of solvents which are characterized bybeing only' slightlysoluble in mineral oils and which have apreferential'se-I lectivity for the primary selective solvent ascompared to the mineral oil. My class of secondary v solvents is furthercharacterized by having a higher internal pressure, and preferably ahigh-s n er boiling point than the primary solvent. The 1 process of myinvention is particularly adapted for the processing of the highlyparaflinic railinate oils. ess decomposition and impairment of thequality of the highly parafimic raffinate oil is avoided since nodistillation of the oil occurs.

The process of my invention may be readily understood by reference tothe attached drawing illustrating one modification of the same. Forpurposes of illustration the feed oil is taken to be a petroleum oilboiling in the lubricating oil- In accordance with the present proc- Thefeed oil upper part of tower I by means of solvent feed line 3.Temperature and pressure conditions are maintained in tower I adapted tosecure the formation of a solvent-poor or rafllnate phase and asolvent-rich or solvent extract phase. mm to be understood that tower Iis provided with suitable distributing and contacting means such ascontact masses, pierced plates, distributing plates and the like. Therafllnate phase is withdrawn from tower I by means of line 4, while thesolvent extract phase is withdrawn from the tower by means of line 5.Water, glycerine or an equivalent solvent modifying agent may beintroduced into tower I at a plurality of stages by means of lines 8, I,8, and 9. The raflinate phase after removal from tower l by means ofline 4 may be cooled in cooler I and then introduced into rafllnatesettler II in which phase separation occurs. The relatively solvent-richphase may be returned to tower I by means of line I2 or withdrawn bymeans of line 30. The relatively solvent-poor rafiinate-oil phase iswithdrawn from' raillnate settler II by means of line I3 and introducedinto railinate extraction tower I4. The

' highly paraflinic oil phase containing phenol dissolved therein ilowsupwardly through tower I4 and' contacts downflowing glycerine which isintroduced into tower illj'by means of line I5. The

drawn from railinate extraction tOWBl. I4 by means of line I6, while theglycerine-phenol phase is withdrawn from tower II by means of line H.The phenol-glycerine phase is introduced into still I8 and distilledunder conditions to remove overhead the phenol, by means of .line 2,which is condensed and recycled to primary tower I. The undistilledglycerine is removed from still It by means of line I and'recycled toraflinate extraction tower I4 by means of line I5.

Although: the present invention is particularly directedandapplicable tothe removal of a priaryfselective solvent from the railinate phase, "maybe applied under certain conditions in the emoval of" theprimaryiselective solvent from the so lent extract phase. .If conditionsshould warthe operation, the procedure employed is "'entiallythe, sameas that used with respect to the "raifinate phase, except that meansmust be "provided for separating any added solvent modifying agent fromthe primary solvent and also from the secondary solvent if it be adifferent material than the latter. However, the removal of the primarysolvent from the solvent extract phase in accordance with the presentprocess is not a preferred procedure. I prefer to use other well knownmeans of removing the solvent from the solvent extract phase. Thus, thesolvent extract phase is withdrawn from countercurrent treating tower Iby means of linev 5, may be cooled in cooler I9, and then passed tosolvent separator '20 in which a phase separation will occur. Therclativelysolvent-poor phase may be returned to tower I by means of line22 or withdrawn from the system by means of line 3|. If the solventextract phase is not cooled, phase separation may be secured by theaddition of a precipitating agent whichis introduced into solventseparator by means of line 28. The relatively solvent-rich raiiinate oilfree of phenol and glycerine is witha phase is withdrawn from solventseparator 20 by means of line 23 and passed tosolvent recovery unit 24.The solvent is removed by means of line,

26, while the highly aromatic extract is removed by means of line 21 andhandled in any manner desirable. It may be desirable to re-extract therailinate phase with glycerine in ramnate extraction tower I4 aftersecuring phase separation of the raflinate in raflinate separator II byintroducing a small quantity of glycerine into the separator by means ofline 29.

The process of the present invention may be widely varied. In general,the process is appli-' cable in the treatment of any mineral oil. It isparticularly adapted for the recovery of primary selective solvents fromhighly parafl'inic ramnate phases in which said selective solvents areof the character which have a preferential selectivity for the morearomatic type compounds as compared to the more parafllnic typecompounds.

I The secondary solvent of my invention is selected from the class ofsolvents, which are characterized by being only slightly soluble inhighly parafllnic mineral oils and which will sub stantially completelydissolve the primary sovent in the presence of said mineral oils. Thesolvents of my invention, furthermore, prefer-- ably have boiling pointshigher than the boilingpoint of the primary selective solvent. Mysolvents are further characterized by having internal pressures in therange between about'7,000' and 14,000 atmospheres. Secondary solvents ofthis character are, for example, glycerine, ethylene glycol, diethyleneglycol, formamide, formic acid, and methyl alcohol. Especially desirablesolvents particularly adapted for the removal of phenolic type primaryselective solvents I from highly paraflinic oil phases are thosesolvents which have internal pressures in the:

sures in the range below about 12,000 atmospheres and whose internalpressures are at least 6,000 atmospheres greater than the internalpressures of the hydrocarbons from which the phenolic type solvent is tobe removed.

Solvent extraction processes involve physical actions instead ofchemical reactions. Therefore, I prefer to classify solvents accordingto ranges of internal pressures, a physical property which isindicativeo1 solvency power, rather than according to a generic chemical namewhich may have little significance. For example, at 20 C. thehydrocarbons have internal pressures in the vicinity of about 2,500atmospheres for parafiins, 3,400 atmospheres for aromatics and 3,000atmospheres for naphthenes, the value for the last being between that ofthe other two as would be expected. Solvents which have the ability toseparate mineral oils into their relatively more aromatic and into theirrelatively more paraflinic constituents have internal pressures in arange higher than the range of the internal pressures of the aromatichydrocarbons.

While there are several may be in the Internal pressure at 20 C, atms.

mmmmm m mm m mmw mmmmmm mmmmmmm 2 3 In general, the temperatures shouldbe Calculated, 112%? It is indirectly measured by such properties assurface tension, heat of vaporization, expansion and compressibility.methods of obtaining the internal pressure of 9.

tion I .=41.4 LD, where I is the internal pressure expressed inatmospheres, L is the energy of vaporization expressed in gram-caloriesper gram. and D is the absolute density expressed in ization isequivalent to latent heat of vaporization minus the energy consumed inexpanding the substance against the external pressure," but the latterfactor is, relatively. quite small and purposes latent heat ofvaporization substituted for energy of vaporization above equation.Since latent heat of vaporization and density both change with a changein temof a substance also changes with a change in its temperature, thevalue becoming greater as the temperature decreases. For convenience andfor purpose of comparison, it is usually preferable to substancesbecause the specific gravities given in the literature are usually forthat temperature. Since latent heats of vaporization are usuallydetermined at temperatures approximating the sequently have no commontemperature basis, the Hildebrand rule may be employed in converting theavailable latent heat values to values having a common temperaturebasis.

Temperature and pressure conditions maintained on the primary extractingtower may vary widely. in the range between the melting point of theprimary solvent and the temperature at which Intent heat ofvaporization- Gm.-cel.lgm.

i. e., as

The

From literature At C.

It is well Table 1 I have found it con- Boiiing Absolute a? 2735 976 4586 4 8w 0 9 0 8 -O 0 LL L 0 180 mwa uu mnn m m mmqmum w nm acwvn mmmamacaw mean auum m 0 0 0 0 0 0 0 0 0 0 0 0 0 LLLLLL LLLLIOO m mu u m mm mmm mm m Solvents having internal pressures at 20 C. above approximately6,500 atmospheres substance,1prefertocalculate it using the equaare notvery satisfactory for extracting mineral low that excessive quantitiesof solvent are re- 10 grams per cubic centimeterrgy of vaporthat theinternal pressure increases with a demay be neglected. Consequently. forpractical aromatic type hydrocarbons and liquids having perature, it isobvious that the internal pressure internal pressures at 20 C. greaterthan about 6,000 atmospheres as secondary solvents following table showsthe internal pressures and calculate the internal pressures at 20 C. forall normal boiling points of a few hydrocarbons and also of some primaryand secondary solvents. It will be noted that water has an internalpressure at 20 C. of 24,250 atmospheres. Although this compound has beenused as a secondary boiling points of the various substances, andconsolvent in certain operations, its very high internal pressure makesit undesirable for the reason that the greater the difference betweenthe internal pressures of two liquids at a given tem- Substance The morecommon solvents used in mineral oil extraction have internal pressuresat 20 C. ranging between about 4,000 and 6,000 atmospheres.

oils to separate them into their more aromatic and more paraflinioconstituents, because the solubility of hydrocarbons in said solvents isso quired to efiect the desired results.

known that solvents are more selective at lower temperatures than athigher temperatures: the reason for this can be explained in the factcrease in temperature.

venient to classify liquids having internal pressures at 20 C. rangingbetween 4,000 and 6,000 atmospheres as primary solvents for the moresolvents suitable for extracting said primary solvents from solutions inhydrocarbons.

perature, the less mutually soluble the two become at that temperature.Thus, for commercial operation a prohibitive amount of water would beneeded to completely remove the primary selective solvent from the oil.

Hydrocarbons:

I III I m I I ImI I I I I I I I I I I Hm I I I. I I at a. in I I I I I wI I I w I I I one n n m m am mms I a m m s I ammm ma age I m wa maa I hV .i m 9 a. eece 1 1 3 w wmms m nm a I nnun .MCMDC m m m mm w 8 h d t OOr N m m mmEDFFMm .n C a P am W At 15 0. Internal pressure .is. the namegiven to the complete miscibility occurs between the oil and force ofcohesion which, together with the -exthe solvent or the oil and thesolvent containing a modifying agent. The quantity of primary solternalpressure, balances the thermal pressure.

vent used per volume of oil likewise will depend to a large extent uponthe particular oil being treated, the solvent employed, as well as uponthe yields and quality of products desired. In gen eral, it is preferredto use from one-half to four volumes of primary solvent per volume ofoil. The temperature and pressure conditions maintained on the secondaryextracting tower likewise will depend upon the above named factors.

. When employing phenol and re-extracting the same with glycerine, it ispreferred that a temperature in the range from 160 I". to 200' F. beemployed.

In order to further illustrate the invention. the following examples aregiven which should not be construed as limiting the same in any mannerwhatsoever:

Example 1- A rafllnate phase containing 12% by volume of phenol securedfrom the extraction of a lubrieating oil with phenol was re-extractedwith glycerine at 180 F. in a countercurrent process consisting of 3stages. A ratio of glycerine to phenolic raflinate of 0.4:1.0 wasemployed. The following table summarizes the results of this operation:

Phenol content of the dephenolized oil' Trace Determined by washing theoil with water and brominating the phenol dissolved therein.

Table 3 Dephenollzed J ttit ve w e ate with Tests on dephenolizedrailinate t n with and subglycerine P blowing wfih natural gas GravityA. P. I 26. 9 8.8 Flash, 385 Viscosity at 100 F. (SUS) 303 Viscosity at210 F. (SUS) 49. 9 Visoosi index 71 Neu tion value 0. 07 0. 07

Both the bromine test for phenol and the neutralization value show thatphenol is readily separated from rafllnate oil by extraction withglycerine. Furthermore, comparison of the A. P. I. gravities of the twodephenolized raflinates shows that substantially no glycerine wasdissolved in the highly paraflinic rafllnate oil. Since the glycerineand phenol content of the dephenolized raflinate was small and since thequantity of dephenolized raillnate recovered was substantially equal tothe quantity of oil charged, it follows that the quantity of oildissolved in the glycerine layer was negligible. This is further borneout by the fact that the solubility of glycerine in mineral oil and ofmineral oil in glycerine is so small as to be very diflicult to measurebut is estimated to beless than about 0.1%. This is likewise true of thelow boiling hydrocarbons, such as benzol, in which glycerine shows veryslight solubility.

In view of the above results, it is evident that phenol can besuccessfully separated from a parafllnic raflinate oil by extractionwith glycerine.

Example 2 The suitability of glycerine as a secondary solvent for theremoval of primary solvents,

particularly from petroleum, may be readily seen by the following data:

Boiling point 554 F.

Specific gravity 1.26

Miscibility with phenol In all proportions at 120 F.

Solubility in ramnate from a Less than 0.2% at Coastal crude A ramnatesecured from a Coastal crude and containing 20% phenol was contactedwith an equal volume of glycerine at 180 F. Under these conditions,approximately 90% of the phenol was removed indicating a 9to 1distribution ratio of phenol between glycerine and oil. This dataindicates that phenol will be efllciently removedby countercurrentextraction with a relatively smaller amount, that is with 30% to ofglycerine.

Example 3 about 0.01%, it may be seen that formamide is a desirablesecondary solvent for removing phenol from a raflinate oil.

Example 4 100 volumes of a mixture containing volumes of Coastal luberafllnate employed in Example ii and 10 volumes of furfural were batchextracted with formamide, using three successive 50% treats at 90 F. Thedesolventized oil contained 0.032% furfural by weight.

Example 6 volumes of a mixture containing 98 volumes of a kerosenerafllnate and 2 volumes of sulfur dioxide were extracted with methylalcohol, using three 50% treats at a temperature range from 0 F. to 10F. The recovered kerosene contained 0.094% sulfur dioxide by weight.

The process of the present invention is not to I be limited in anymanner whatsoever, but only in and by the following claims in which itis desired to claim all novelty in so far as the prior art permits.

I claim:

1. Process for the removal of primary selective solvents from raifinateoils secured in the solvent treatment of petroleum oils, said primarysolvents Since the being of the class of solvents which has the abilityto selectively dissolve the more aromatic constituents as compared tothe relatively more paramnic constituents comprising treating saidrafilnate oils containing said primary solvent with formamide underconditions to form a substantially solvent-free rafilnate oil phase anda primary solvent formamide phase, removing the oil phase and separatingthe primary solvent from the Iormamide.

2. Process in accordance with claim 1 in which said primary solvent isphenol.

3. Solvent treating process comprising contacting a petroleum oil with aselective solvent having the ability to selectively dissolve the more 15JOE 1|. FRANKLIN, JR.

